Three dimensional (3D) cultures provide innovative approaches to study processes that contribute to tumorigenesis because they recapitulate cancer cells in their native in vivo environment. The majority of the supporting data that posits the importance of tumorigenesis has been obtained using two dimensional (2D) cell culture systems. Cells in 2D are subjected to unnatural mechanical and geometric constraints that do not represent the three dimensional (3D) milieu of a tumor. The complex interplay between biochemical, and mechanical properties may be undermined or compromised in 2D cultures and may affect many important functions such as gene and protein expression. Considerations on the mechanical, biochemical and physical properties of any 3D system, aim to mimic the native ECM. One of the major advantages is the potential for rapid experimental manipulation achieved by controlling these parameters that can permit development of sophisticated cancer models. Tailored 3D cell culture scaffolds combining relevant platforms with multiple bio-functionalities will allow for the specific induction of signal transduction pathways, the sorting of different cell types, or the control of cancer cell differentiation. Combination of existing 3D systems that impart separate yet important characteristics that preserve structural and functional in vivo-like complexity to the whole will increase the sophistication of these 3D models. Presently, there exist a significant need for more realistic tumor models to study tumorigenesis and the effective screening of anticancer drugs.
The most commonly used 3D model are spheroids that are used for a variety of experimental studies in chemotherapy and radiotherapy and are being pursued in high throughput screening (HTS) programs for drug development, candidate efficacy and safety. Spheroids impart functional and mass transport properties similar to those observed in micrometastases or poorly vascularized regions in solid tumors (Hirschhaeuser et al., (2010) J. Biotechnol. 148: 3-15). These features combined with the complexities of cell-cell and cell-matrix interactions, affect the uptake, penetration, distribution and bioactivity of therapeutic drugs. They are simple 3D structures that can be generated from a wide range of cell types, and form due to the tendency of adherent cells to aggregate and are typically created from single or co-culture techniques such as hanging drop, rotating culture or conclave plate methods to name a few (Pampaloni et al., (2007) Nat. Revs. Mol. Cell Biol. 8: 839-845; Timmins et al., Cell Tissue Res. 320: 207-210; Castaneda & Kinne (2000) J. Cancer Res. Clinical Oncol. 126: 305-310).
The inherent limitation of this model is that it is entirely cell based and do not represent the mechanical features of the ECM as a whole. To address this issue various substrates or scaffolds derived from biological, natural or synthetic sources have been used to form hydrogels, films, fibers, micromolded structures in microfluidic devices, and microchips in the construction of spheroids. For example, hepatocytes self-assemble to form spheroids on scaffolds made from alginate, hyaluronic acid, peptide scaffolds, and galactosylated meshes (Gurski et al., (2009) Biomaterials. 30: 6076; Gurski et al., (2010) Biomaterials. 31: 4248; Elkayam et al., (2006) Tissue Engineering 12: 1357-1368; Shin et al., (2012) Biotech. Letts. 34: 795-803; Wang et al., (2011) Biomacromolecules 12: 578-584; Chung et al., (2002) Biomaterials 23: 2827-2834; Ivascu & Kubbies (2007) Int. J. Oncol. 31: 1403-1413; Horning et al., (2008) Mol. Pharmaceutics 5: 849-862; Semino et al., (2003) Different: Res. Biol. Diversity 71: 262-270; Chua et al., (2005) Biomaterials 26: 2537-2547).
Incorporation of spheroids into synthetic 3D polymeric scaffolds has been used as a model for screening anticancer drugs (Ho et al., (2010) Cancer Sci. 101: 2637-2643). These scaffolds provide support for the spheroids thereby mimicking the physical interaction of the tumor with the topographical features of the native ECM, as for example, between the tumor and the basement membrane.
The interaction of mammalian cells with sub cellular topography has proven to be an important signaling modality in controlling cell function via mechanotransductive cues. The tumor microenvironment consisting of tumor cells and corresponding stroma intimately associate with the physical structures of the ECM during all stages of tumorigenesis. Synthetic substrate topography has been shown to influence cell migration, differentiation, and gene expression. For example, SAL/N cancer fibroblasts cultured on micropatterned PDMS and C6 glioma cells cultured on polystyrene periodic structures exhibit differences in morphology, proliferation and migration in response to various topographical cues (Tzvetkova-Chevolleau et al., (2008) Biomaterials 29: 1541-1551; Wang et al., (2006) J. Biomed. Mats. Res. Part A. 78A: 746-54).
Electrospinning is a versatile technique used to produce polymeric fibrous scaffolds for cell culture applications. It allows for the preparation of unique matrices of aligned or non-woven meshes containing nano to micrometer sized fibers using diverse materials and fabrication techniques (Zanatta et al., (2012) Brazilian J. Med. Biol. Res. 45: 125-130; Zanatta et al., (2012) J. Biomed. Nanotechnol. 8: 211-218; Yu et al., (2012) Carbohydrate Polymers 90: 1016-1023; Tsai et al., (2012) PloS one. 7: e31200; Sundaramurthi et al., (2012) Biomedical Materials 7: 045005; Samavedi et al., (2012) Biomaterials; Meinel et al., (2012) Eur. J. Pharmaceut. Biopharmaceutics. 81: 1-13). Studies have shown that modified electrospun scaffolds simulate favorable functional responses in cancer cells (Agudelo-Garcia et al., (2011) Neoplasia 13: 831-896; Johnson et al., (2009) Tissue Engineering Part C-Methods 15: 531-540; Xie & Wang (2006) Pharmaceut. Res. 23: 1817-1826).